A vinyl chloride-based polymer is a polymer including 50 wt % or more of a repeat unit derived from a vinyl chloride monomer (VCM), which is low in cost, easy to control hardness, and applicable to most processing apparatuses, so that the application fields are diverse. In addition, the vinyl chloride-based polymer may provide a molded body excellent in physical and chemical properties such as mechanical strength, weather resistance, chemical resistance and the like, and thus is widely used in various fields.
Such a vinyl chloride-based polymer is produced in a different form depending on the use. For example, a vinyl chloride-based polymer for straight processing such as an extrusion process, a calendering process, and an injection process is generally produced by suspension polymerization, and a vinyl chloride-based polymer for paste processing such as dipping, spraying and coating is produced by emulsion polymerization.
In the paste processing, a vinyl chloride-based polymer latex for paste processing obtained by emulsion polymerization is generally dried by spray-drying to form final resin particles. The particles are dispersed in a solvent or a plasticizer and then subjected to a process such as coating (reverse roll-coating, knife coating, screen coating, spray coating), gravure and screen printing, rotation casting, and shell casting and dipping, and thus applied to products such as flooring, wallpaper, tarpaulin, rainwear, glove, automobile underbody coating, sealant and carpet tile.
This vinyl chloride-based polymer for paste processing alone is difficult to apply because of low processability and is usually used by being processed into a plastisol form which is composed of various additives such as a heat stabilizer together with the plasticizer. In this case, it is important that the viscosity of the plastisol is adjusted to an appropriate level to maintain good flowability.
Meanwhile, prior to the improvement of flowability, when an external force (shear rate) is not applied, the plastisol maintains a gel state in which the plastisol does not flow, and as the external force (shear rate) is applied, the plastisol is changed into a flowable plastisol. The higher a Bingham yield stress value to be appeared in this case, the more clearly the gel state in which the plastisol does not flow when no external force is applied is exhibited. In addition, in the case of the flowable plastisol of which viscosity is lowered due to applying the external force, when the external force (shear rate) is removed again, the plastisol is restored to the original gel state. As the Bingham yield stress value in this case becomes the same as a Bingham yield stress value in the case of applying the external force, gel properties are similar to those of the original plastisol. When such thixotropy is poor, there is a problem that the processability and productivity are deteriorated resulting from the viscosity change of the plastisol during processing of the plastisol. Also, when the external force is increased or decreased, in the case of the Bingham yield stress being very high, the viscosity is very high during solation of the gel and thus the flowability is not good, and in the case of the Bingham yield stress being very low, there is a problem that the gel state holding ability of the plastisol is lowered and the processability is deteriorated.
In order to solve the above problem, there has been proposed a method of adding an additive such as an inorganic material in the production of a plastisol, but the method has a problem of deteriorating the mechanical properties of a molded article. Accordingly, there is a continuing need for the development of a vinyl chloride-based polymer composition excellent in thixotropy while preventing the mechanical properties of the molded article from deteriorating.